Re: Using Curl to send a HTTP request to a local OSRM Server from an AGL service

["Denis Marin" <dvmarin@xxxxxxxxxx>]

Hello Sebastian,

Regarding code snippets provided recently. Please bear in mind that the callback for JSON downloads is oversimplified and will only work well for short payloads. 

Actually CURL documentation says, that it might be called multiple times for single payload. This means that sometimes on first call you will receive a half of your JSON, and on second time another half of it, each half is not a valid JSON :\

You might want to use some pre-allocated buffer plus write pointer in it to receive data.

OR you can let CURL and standard library do all this for you by using NULL as CURLOPT_WRITEFUNCTION and use open_memstream to allocate memory buffer which is writable like a file.

the whole download_json is below. just throw away the callback and you are safe.

struct json_object* download_json(const char* link)

{

CURL* curl_handle = curl_easy_init();

char* buf = NULL;

size_t buffer_size;

FILE* json_filestream = open_memstream(&buf, &buffer_size);

curl_easy_setopt(curl_handle, CURLOPT_URL, link);

curl_easy_setopt(curl_handle, CURLOPT_WRITEFUNCTION, NULL); // use default fwrite

curl_easy_setopt(curl_handle, CURLOPT_WRITEDATA, json_filestream); // file pointer to default fwrite

curl_easy_setopt(curl_handle, CURLOPT_FAILONERROR, 1);

curl_easy_setopt(curl_handle, CURLOPT_TIMEOUT_MS, 500);

(void)curl_easy_perform(curl_handle);

fclose(json_filestream); // now buf and buffer_size are valid

struct json_object* result = json_or_null(buf, buffer_size);

free(buf); // buffer allocated by open_memstream must be freed as per man(3)

curl_easy_cleanup(curl_handle);

return result;

}

BRs,

Denis.

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От: agl-dev-community@xxxxxxxxxxxxxxxxxxxxxxxxx <agl-dev-community@xxxxxxxxxxxxxxxxxxxxxxxxx> от имени sebastian_alois.eckl@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx <sebastian_alois.eckl@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
Отправлено: 25 мая 2021 г. 19:24:54
Кому: agl-dev-community@xxxxxxxxxxxxxxxxxxxxxxxxx
Тема: Re: Using Curl to send a HTTP request to a local OSRM Server from an AGL service

 

Hello Denis,

thanks alot for your reply, that definitely helps. I'll give it a try.

Best regards

Sebastian

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